Conventionally, as regards a network in which a plurality of independent paths are set between a transmission side transfer device and a reception side transfer device, studies have been conducted on a scheme for enhancing its reliability. The transmission side transfer device specifies a frame that requires reliability enhancement (which will be referred to as “important frame”) with reference to information in the frame header. Then, the transmission side transfer device inserts identifiers, such as transmission source identification information, path information, and/or order information, into the important frame, and performs broadcast transmission to all the independent paths. The reception side transfer device specifies an important frame from frames received from the independent paths. The reception side transfer device identifies an important frame having the same information based on a frame identifier, and then selects whether to perform transfer or discard. As a result, even if a failure occurs at one of the paths and thereby disconnects frames, an important frame can be communicated without causing instantaneous interruption, by use of another of the paths if it remains. Such a technique is disclosed in Patent Literature 1 listed below.
According to SPB (Shortest Path Bridging), all the transfer devices involved therein recognize the connection configuration and the instruments respectively connected to the transfer devices, whereby a shortest path tree (Shortest Path Tree) using VLAN-ID (Virtual Local Area Network-IDentify), (which will be referred to as “VID”, hereinafter), is configured by use of a path control technique called “IS-IS” (Intermediate System to Intermediate System). A transmission side transfer device transmits a frame, after performing thereto an encapsulation process, which contains a path and destination information. A reception side transfer device serving as the destination performs transfer to a subordinate instrument, by outputting a frame after performing thereto a decapsulation process. As a result, also in a mesh network, frames can be transferred between transfer devices through the shortest path and at the minimum cost. Such a technique is disclosed in Non Patent Literature 1 listed below.